Formal Comment The Shoe Fits, but the Footprint is Larger than Earth

William E. Rees1*, Mathis Wackernagel2 1 University of British Columbia, School of Community and Regional Planning, Vancouver, British Columbia, Canada, 2 Global Footprint Network, Oakland, California, United States of America

In their Perspective in this issue of PLOS Biology, Blomqvist et al. They nevertheless constitute the most comprehensive assessments of the [1] set out to demonstrate that ‘‘Ecological Footprint measure- ecological status of nations available. ments, as currently constructed, are so misleading as to preclude Independents tests of the method are, of course, essential. In the their use in any serious science or policy context.’’ Should the past few years over a dozen national and international government reader be confident in this assessment or are Ecological Footprint agencies have reviewed the National Footprint Accounts for their methods and results adequate to guide sustainability policy? countries (see www.footprintnetwork.org/reviews). The French Their Perspective, ‘‘Does the Shoe Fit?’’, does not question the Ministry of Sustainable Development, for example, independently fundamental purpose of Footprint accounting. The method is recalculated the French Footprint from 1961 to today obtaining designed to estimate human demand for biocapacity, defined as: results within 1–3 percent of Global Footprint Network’s ‘the aggregate area of land and water ecosystems required by assessments [8]. specified human populations to produce the ecosystems goods and services they consume and to assimilate their carbon wastes.’ The Writers’ Diversion Footprint accounting is thus based on the premise that the regenerative capacity of the ecosphere is associated with produc- Blomqvist et al. ignore national and regional Footprint tive ecosystem area. The production of food and fibre; the assessments on grounds that these merely assess ‘‘self-sufficiency’’. urbanization of once agricultural or forested lands; and the Instead they jump straight to the global scale. sequestration of that portion of carbon emissions from fossil fuels This is problematic. National/regional Footprint assessments that is not already absorbed by oceans or by long-term reveal some of the most significant findings of Footprint sequestration strategies in agriculture or forestry, all constitute accounting and those with the highest policy utility. Even competing or non-overlapping uses of ecosystems. (Typically, one relative ‘‘self-sufficiency’’ is becoming an increasingly important cannot simultaneously use paved-over land for food production or policy consideration in an era of accelerating global change as forest products; today’s cropland and commercial forests are revealed by rapid growth in international ‘land-grabbing’ by usually carbon sources, not sinks). We estimate and sum these countries with ecological deficits [9]. Also, most policy-oriented separate areas to estimate study populations’ total Ecological Footprint studies are carried out at the city, regional, and Footprints. national levels because they correspond to levels of government Global Footprint Network has developed national Footprint that have authority to act. (There is no corresponding global accounts, using consistent United Nations data sets to provide both authority.) The method currently shows that about 84% of the Footprint and biocapacity assessments of most nations [2–4]. One world population live in countries that run growing ecological can therefore readily compare national and global Footprints with deficits, i.e., they are living on overuse of their own ecosystems, domestic and global supplies of biocapacity, respectively. This on imported biocapacity or on appropriations from the global comparison helps to shed light on core research questions commons [4,9]. Only a few countries have significant biocapa- fundamental to human wellbeing and sustainability: How does a city reserves and these resources are largely already taken up in population’s consumption-based demand compare to its domestic satisfying the deficits of net-importing countries. For example, biocapacity? Is the population dependent on local overuse, net- the domestically unused half of Canada’s cropland, commercial imports, or net-appropriations from the global commons? How do forest land, and fisheries are presently committed to export various nations/populations compare and what are the trends over markets [10,11]. Whether running an ecological deficit in an time? At the global scale, is H. sapiens living within the regenerative uncertain world already in overshoot is a significant risk every means of nature? nation must evaluate for itself. However, there is nothing gained Global Footprint Network’s most recent accounts reveal that by not knowing one’s country’s biocapacity balance, and there Earth’s biocapacity in 2008 was 12 billion hectares (ha) compared to humanity’s Footprint of 18.2 billion ha, and that the average Ecological Footprint had reached 2.7 global hectares (gha) per Citation: Rees WE, Wackernagel M (2013) The Shoe Fits, but the Footprint is capita compared to only 1.8 gha of available biocapacity per Larger than Earth. PLoS Biol 11(11): e1001701. doi:10.1371/journal.pbio.1001701 capita [5]. (A global hectare is a hectare of global average Academic Editor: Georgina M. Mace, University College London, United productivity.) This difference means that humanity is in ecological Kingdom overshoot, currently using at least 50% more of nature’s goods and Published November 5, 2013 services than ecosystems regenerate [5–7]. These national Copyright: ß 2013 Rees, Wackernagel. This is an open-access article distributed Footprint estimates are conservative since data limitations prohibit under the terms of the Creative Commons Attribution License, which permits consistent adjustments to account reliably for the over-exploitation unrestricted use, distribution, and reproduction in any medium, provided the of ecosystems (see below), and carbon dioxide, mainly from fossil original author and source are credited. fuel and cement production, is the only waste stream considered. Funding: The authors received no specific funding for this work. Competing Interests: We have an interest in this issue because we are the developers of Ecological Footprint accounting, which is being criticized in the Formal Comments are critiques of specific published articles. manuscript to which Dr. Rees was invited to respond. * E-mail: [email protected]

PLOS Biology | www.plosbiology.org 1 November 2013 | Volume 11 | Issue 11 | e1001701 are presently no better estimates than those delivered by Global carbon per ha per year [12]). We can thus readily estimate the Footprint Network’s current Footprint accounts. global carbon Footprint and demonstrate overshoot. While Blomqvist et al. do not contend the global carbon-sink What Footprint Estimates Measure deficit (the only part of the Footprint accounts they review), they seem to dismiss its relevance on grounds that if the estimated Many of Blomqvist et al.’s claims are themselves misleading. For natural carbon sequestration rate were increased to instance, they assert that ‘‘… the ecological footprint is practically 2.6 t ha21 yr21, ‘‘the entire global ecological overshoot disappears’’ equal to the carbon footprint’’. This is incorrect. The carbon and, following on, that technological fixes such as wind and Footprint is only a small fraction of the domestic Footprints of solar energy might also reduce or offset carbon emissions. These many countries (e.g., 7% in the case of Tanzania in 2008) and assertions warrant two comments. First, while spatial and constitutes just 55% of the total human Footprint in 2008 (up from temporalvariationincarbonsequestration is significant, our 35% in 1961) [4,5]. carbon Footprint is based on current best estimates of de facto These authors also note that ‘‘none of the five non-carbon average sequestration rates, not on what might be the case if the land-use categories has any substantial ecological deficit – world’s forests consisted of managed high-yield forest planta- suggesting that the depletion of cropland, grazing land, forest tions. In any case, the carbon sequestration rate is not land, and fishing grounds is not occurring on an aggregate, 2.6 t ha21 yr21 or no carbon dioxide would be accumulating global level.’’ In interpreting this observation, the reader must in the atmosphere. Second, the criticisms made by Blomqvist’s consider three facts. First, the global Footprint of cropland, et al. indirectly suggest policy recommendations based on global built-up land, and grazing land as currently measured can only be Footprint results (despite their claim that the Footprint is not less than or equal to the respective biocapacity. Unlike nations policy relevant); namely, develop dedicated carbon sink forest and regions, Earth cannot ‘import’ cropland biocapacity and plantations of fast growing species (with a sequestration rate of, therefore cannot show a deficit; given a total of 4.5 billion 21 21 hectares of active cropland, one cannot harvest from 5.5 billion say, 2.6 ha yr ) and a crash program of renewable energy ha. Second, current cropland, forest land, and marine development to help eliminate the present carbon emissions Footprints do not, in fact, reflect depletion but this does not overshoot. Of course, with the implementation of such imply that there is none. We fully recognize that local ecosystem programs, future Footprint assessments would show the corre- abuse is a significant problem and that Footprint accounts sponding deficit reduction. should reflect biocapacity losses due to land/soil degradation and over-fishing. If we could applythis‘fix’,itwouldcertainly Conclusions increase our estimates of ecological deficits. However, to make Despite Blomqvist et al.’s reservations, Footprint results show reliable adjustments would require globally consistent data sets, that: (1) most countries are in ecological deficit, increasingly which do not exist. It is worth noting in passing that this lack dependent on potentially unreliable trade in biocapacity; (2) suggests an important global-level policy recommendation, humanity is at or beyond global carrying capacity for key namely, the world’s nations should commit to assessing land/ categories of consumption, particularly agriculture (factoring in ecosystem degradation using standardized methods to enable us soil loss and ecosystem degradation would reveal additional to apply a ‘sustainability factor’ to our present eco-Footprint deficits); (3) global carbon waste sinks are overflowing; and (4) estimates. The third and final fact is that there is no the aggregate metabolism of the human economy exceeds the inconsistency between the existence of reserves in some global regenerative capacity of the ecosphere (and the ratio is increasing). biocapacity categories and the fact of local ecosystem degrada- Significantly, Blomqvist et al. indirectly suggest several globally tion. Total biocapacity can exceed the harvest Footprint even relevant policies to improve Footprint accounts and to reduce though the exploitation of various fish stocks or forest humanity’s carbon footprint. How, in this light, the authors of the ecosystems exceeds local regenerative capacity. Perspective can conclude that the results of Footprint estimates are The situation is different for the carbon Footprint. We have ‘‘…so misleading as to preclude their use in any serious science or relatively strong national and global data on carbon dioxide policy context’’ remains unclear. What could we possibly gain by emissions, mostly from burning fossil fuel and cement production; accumulations in the atmosphere show unequivocally that ignoring Footprint assessments in national and global policy- emissions far exceed the sequestration capacity of the ecosphere. making? We also have acceptable estimates of sequestration rates by average forest ecosystems based on an extensive literature review, Author Contributions on Food and Agriculture Organization and Intergovernmental The author(s) have made the following declarations about their Panel on Climate Change reports (approximately1 metric ton contributions: Wrote the paper: WER MW.

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